Study of the Influence of Operating and Geometric Parameters on the Critical Outflow of Subcooled and Boiling Water through Channels of Different Geometry

The scientific and technical literature presents a large number of works dedicated to the experimental study of the critical out flow of saturated and subcooled liquid through cylindrical channels. Despite this, the available sources do not provide an assessment of the extent to which certain geometric parameters and operating conditions of experiments affect the critical outflow. This article is aimed at the analysis of experimental data using statistical methods and machine learning on critical outflow obtained at Elektrogorsk Research and Development Center (EREC, Russia). The purpose of the work is to identify statistical relationships between operating and geometric parameters, as well as to quantify the influence of these parameters on the critical mass flow rate and pressure. The analysis of experimental data for channels with a filleted inlet edge showed a strong influence of the inlet edge shape both on the value of the critical mass velocity and on the final pressure in the outlet section of the channel, which is established at the critical outflow mode. A comparison of the experimental data for channels with different shapes of the inlet section with the same operating and other geometric parameters showed that for channels with a rounded inlet edge, the critical mass velocity is approximately 25% higher than for channels with a sharp inlet edge. As the nozzle throat length increases, this difference decreases asymptotically. Among the regime parameters, the main contribution to the dispersion of the critical mass velocity is made by the undersaturation (subcooling) of the medium at the inlet which comprised 51% of the total influence of the regime and geometric parameters. An increase in the undersaturation and a decrease in the length of the channel throat lead to decrease in the back pressure necessary to establish the critical outflow mode. In extreme cases, the critical pressure ratio (outlet/inlet) can be 0.1, which is significantly lower than the generally accepted value of 0.5 in engineering practice. The results obtained can be used in the future for design of experiments aimed at expanding the range of operating parameters or optimization elements whose operation is based on the phenomenon of critical outflow.